Preparation of nitrocellulose



Patented Dec. 5, 1939 UNITED STATES PREPARATION OF NITROCELLULOSE George A. Richter, Berlin, N. H., assignor to Brown Company, Maine Berlin, N. H., a corporation of No Drawing. Application May 8, 1937,

' Serial No. 141,555

6 Claims.

etc., which can cause partial gelatinization of paper fragments and induce marked shrinkage therein when they are dried. However, a preferred reagent for the purposes hereof is caustic soda solution of mercerizing strength at the particular temperature at which it is applied to the paper fragments, as a mercerizing solution not only induces the shrinkage or physical change deshed in the paper fragments but also purifies the cellulose fiber of which such fragments are composed, thereby enabling the realization of high grade nitrocellulose, whose quality is comparable to that realized from cotton, from paper fragments composed of wood pulp or other cellulose fiber with which is associated a significant percentage of non-alpha-cellulose constituents lending themselves to extraction or dissolution to a considerable degree in the niercerizing solution.

By reason of the marked-shrinkage induced in paper fragments subjected to the treatments hereof preparatory to nitration, such fragments are distinctly strengthened or toughened; and they hence donot tend to disintegrate during nitration into fine particles or shreds apt to be lost during the nitration or after-nitration treatments and thus conducing to lower than expected nitrocellulose yield. Indeed, the invention hereof enables the realization of excellent nitrocellulose yield even from paper fragments composed of low-viscosity cellulose fiber, which, by reason of treatment with dilute aqueous mineral acid solution, oxidant solution or similar viscosity-reducing agent, has become sufficiently embrittled to impart tendency toward disintegration to paper formed from such fiber. By inducing marked shrinkage in such paper fragments and thereby increasing their strength or toughness, disintegration thereof during the nitration and/or after nitration treatments can be practically completely obviated. t might be noted that the marked shrinkage induced in the paper fragments hereof is attended also by their curling or puckering to such an extent that they do not tend to pack face to face in the nitrating bath; and this means both that the nitrating acid is given opportunity to diffuse rapidly and substantially uniformly into and throughout-the bodies of the fragments and'that the acid is more readily and completelydrained therefrom after nitration, especially when the so-called water-displacement method of draining the nitrating acid from the nitrated mass of fragments is employed and when the water is similarly displaced by alcohol or equivalent dehydrating medium.

The practice hereof will now be described in terms of treatment of paper fragments with a mercerizing' solution under conditions leading to dried, mercerized'fragments nitrata'cle into so-called high-viscosity nitrocellulose. The paper sheet employed as starting material for such purpose is preferably composed of white, refined wood pulp of an alpha-cellulose content upwards of about 93%, but, if desired, high grade bleached sulphite pulp and bleached kraft pulp may serve as the cellulose of such sheet. The paper sheet may be slit, as it is being progressively LlIlWOllIld from a roll, into narrow strips or'ribbons, for instance, of about V to A inch Width, and the strips then out transversely into paper fragments of, say, about 1 to 2 inches length' A mass of the resulting paper fragments may then be steeped in caustic soda solution of about 16% to 20% strength at a temperature of about 15to 20 C. ifv desired, the causticity of the solution may be as low as about 10%, provided that it is applied at sufficiently low temperature to effect the desired marked mercerizing action on the paper fragments, say, at about 10 C. However, when a solution of a causticity even as low as about 10% is applied at too low a temperature, say, 5 C., it is quite diiii-, cult to maintain the integrity of the paper fragmentsby reason of the tendency of the fragments .to disintegrate into a mush under the intense swelling and meroerizing action thereupon of the solution at such low temperature. It is, accordingly, desirable to work with solutions having the desired mercerizing activity under combined causticity and temperature conditions conducive to the maintenance without difficulty of the integrity of the paper fragments. The solution penetrates the mass and its individual fragments practically instantly; and, after a soaking period of about 15 to 30 minutes, free caustic soda solution may be removed from the mass, as by centrifugation or equivalent treatment. Thus, the mass of solutionsoaked fragments may be heated somewhat, for

instance, to a temperature of about 50 C., preparatory to its centrifugation so as to facilitate removal of solution therefrom. While the moist,

centrifuged fragments are still in the centrifuge, they may be washed with water, preferably heated to a temperature of, say, about 50 C., until practically no alkali residue remains therein, whereupon dilute sulphurous acid solution or its equivalent and wash water may be successively run into the centrifuge in volumes suflicient to insure neutralization of residual traces of alkali and elimination of the products of neutralization. The

finally washed and centrifuged 'mass of paper fragments may then be dried in any suitable way,- for instance, as in a hot-air chamber or tunnel,

The dried fragments have a puckered appearance and a comparatively harsh feel, but they are very readily and substantially uniformly penetrated by nitrating acid, water, and other reagents. When a mass of the fragments is nitrated with the usual mixed nitrating acid containing, say, about 24% nitric acid, at a temperature of about 30 to 40 C., a high nitrocellulose yield is had with low acid retention. The nitrocellulose is of excellent qual ity and dissolves readily in the usual nitrocellulose solvents to form solutions of substantially perfect clarity. The nitrocellulose *thus produced does not differ appreciably in viscosity from nitrocellulose prepared from the original or untreated paper.

The inventive principles hereof are also applicable when so-called low-viscosity nitrocellulose is in view. For such purpose, the paper sheet may be composed of cellulose pulp that has undergone bleaching or other treatment under conditions imparting thereto a viscosity of, say, about 0.4 to 4.0 poises, as measured by the standard method of producing and testing a cuprammonium-cellulose solution. The paper may be cut into fragments, as already described; and a mass of the fragments may then be steeped in caustic soda solution of about 18% to 25% strength containing about 15% or more sodium hypochlorite bleach or equivalent oxidant, based on the dry weight of paper, and at a temperature of about 45 to 60 C. After a soaking treatment of about two hours, when it is found that the viscosity of the cellulose has been reduced to about 0.1 poise, the mass of paper fragments may be centrifuged, washed, and otherwise treated as previously described. Upon nitrating the resulting dried, mercerized paper fragments in the usual mixed nitrating acid but at a temperature of, say, 50 C., nitrocellulose of 12% nitrogen content is had; and such nitrocellulose dis,- solves in the usual nitrocellulose solvents to form solutions of a viscosity comparable to those realized from the so-called half-second nitrocelluloses currently being marketed.

It might be noted that the preparation of low Viscosity nitrocellulose might involve the use of cellulose-pulp whose solution viscosity has been so markedly reduced by suitable chemical treatment prior to forming it into waterleaf paper that the paper subsequently subjected to the processing sired in the nitrocellulose.

or shreds.

hereof in fragment form need be treated with mercerizing solution containing little, if any, oxidant to yield the desired low viscosity nitrocellulose. On the other hand, if the waterleaf paper has been formed from. cellulose fiber of normal solution viscosities, that is, from fiber which has not undergone a special chemical treatment designed to lower markedly its solution viscosity, the mercerizing solution subsequently applied to the paper in fragment form should, as indicated in the example already given, contain an amount of oxidant capable of reducing the solution viscosity of the fiber to the low value desired.

It is-possible to depart in various respects from the particular examples of. procedure hereinbefore described. Thus, the causticity and/0r temperature of the mercerizing solution for treating the paper fragments may vary, but, in any event, the causticity and temperature of the solution are correlated so as to cause, marked mercerization of the cellulose fiber and thus induce the desired marked shrinkage in the paper fragments when they are dried. A caustic soda solution of about 15% to 25% strengthmay ordinarily be used to good advantage at a temperature of about 15 to 50 C., but the strength of the solution and/or the temperature. at which it is applied may be higher or lower in instances when special characteristics are to be imparted to paper fragments. treatment of about 30 minutes is usually all that is necessary in the case of waterleaf paper ofcom- A time of paratively porous'or open structure, when the paper fragments being treated are to be converted into a high-viscosity nitrocellulose, but in those even longen'and the solution is preferably heated to a temperature of, say, about 50 C. The amount of oxidant added to the mercerizing solution is, as already indicated, also subject to variation, depending upon the particular viscosity de when high-viscosity nitrocellulose is being produced, it may be desirable to add to the merceriz- On the other hand,-

ing solution a suitable amount of sodium sulphide,

sodium sulphite, or other reducing agent to minimize oxidative eifect on the fiber and attendant reduction of its solution viscosity. Other secondary chemicals may be added to the mercerizing caustic soda solution. For instance, carbonbi sulphide may be added thereto in very small amount designed to increase swelling of' the fiber and to enhance subsequent shrinkage of the paper fragments while avoiding such amount of carbon bisulphide as would cause sensible solution of fiber as cellulosexanthate.

Because the paper fragments are strengthened nitration, such treatments as bleaching, washing,

Indeed, the mercerized paper fragmentshereof may even undergo, preparatory to neutralization with weak acid solution, another washing, and final dry. The dried fragments. lend themselves nicely to storage and shipment,

to include relatively thin waterleaf papers of a basis weight of, say, 30 to 50 pounds and thicker l papers or boards, for instance, so-called pulp:

boards or drier sheets. The compactness of the paper or pulp sheets used herein may range from, say, about to about 100. The compactness values given herein represent the ratio of basis weight to the sheet thickness in inches multiplied by the factorlO- The basis weight values given herein represent the weight in pounds of 415,000 square inches of sheet material. The term fragments as used herein is to be construed as meaning relatively small pieces of paper or pulpboard chips; and while elongated pieces or fragments of paper were described in the examples by reason of the fact that they can be baled and otherwise handled to good advantage, it is to be understood that the pieces or fragments might take the form of squares and other shapes.

It has been proposed in the prior art to nitrate paper after it has been conditioned by a method involving the passage of a progressively moving sheet through a bath of mercerizing solution, thence through a bath of wash water, and thence over drier drums or the like. In such a method, free shrinkage of the paper sheet is restrained and the paper sheet remains in contact with the mercerizing solution for only an exceedingly short period of time. The method hereof not only requires far less expensive equipment but makes possible far longer contact between the mercerizing solution and the paper and, accordingly, more pronounced mercerizing and purifying action on the paper; and, because the paper is mercerized and subsequently dried in fragment form and is under no restraint or tension during drying, it can shrink and pucker far more pronouncedly and thus, upon nitration, yield the improved results already indicated.

I claim:

1. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a bases weight ranging from about 30 to about pounds, which comprises cutting the paper into fragments of a minimum span in the order of magnitude of about A; to inch, treating a mass of such fragments with a mercerizing solution for a period of at least about fifteen minutes, washing the fragments substantially free from mercerizing solution, drying them, and nitrating the dried, .mercerized fragments.

2. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a basis weight ranging from about 30 to about 100 pounds, which comprises cutting the paper into fragments of a minimum span in the order of magnitude of about /8 to inch, steeping a mass of such fragments in a mercerizing solution for a period of at least about fifteen minutes, removing free mercerizing solution from the resulting solution-soaked fragments, washing the fragments substantially free from the mercerizing solution,

drying them, and nitrating the dried, mercerized fragments.

3. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a basis weight ranging from about 30 to about 100 pounds, which comprises cutting the paper into drying them, and nitrating the dried, mercerized fragments.

4. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a basis weight ranging from about 30 to about 100 pounds, which comprises cutting the paper into fragments. of a minimum span in the order of magnitude of about to A inch, treating a mass of such fragments at elevated temperature with a .mercerizing solution containing an oxidant of the nature of hypochlorite for a period of at least about fifteen minutes, washing the fragments substantially free from such mercerizing solution, drying them, and nitrating the dried, mercerized fragments.

5. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a basis weight ranging from about 30 to about 100 pounds, which comprises cutting the paper into fragments of a minimum span in the order of magnitude of about to inch,.treating a mass of such fragments with a chemical solution capable of effecting a gelatinizlng action on cellulose fiber for a sufficient period of time to cause partial gelatinization of the fragments to such a degree that the fragments upon subsequent drying undergo at least 10% to 20% shrinkage in the area originally presented thereby, drying the fragments, and nitrating the dried, mercerized fragments.

6. A process of preparing nitrocellulose from cellulose fiber in the form of paper of a-basis weight ranging from about 30 to about 100 pounds, which comprises cutting the paper into fragments of a minimum span in the order of magnitude of about A; to 4 inch, treating a mass of such fragments with a chemical solution capable of effecting a gelatinizing action on cellulose fiber for a sufficient period of time to cause partial gelatinization of the fragments to such a degree that the fragments upon subsequent drying undergo at least 10% to 20% shrinkage in the area originally presented thereby, washing the partially gelatinized fragments substantially free from chemical-solution, drying them, and nitrating the dried, mercerized fragments.

GEORGE A. RICHTER. 

